For example, inductive position-measuring devices may take the form of inductive rotary encoders for determining the angular position of two machine parts rotatable relative to each other. In inductive rotary encoders, exciter windings and receiver coils are applied, for instance, in the form of printed conductors on a shared printed circuit board that is fixedly joined, for example, to a stator of a rotary encoder. Opposite to this printed circuit board is a further board in the form of a code disk, on which electrically conductive and non-conductive surfaces are applied as a graduation region or graduation structure in alternation at periodic intervals, and which is joined in rotatably fixed fashion to the rotor of the rotary encoder. When an electrical exciter field, changing over time, is applied to the exciter windings by imparting an excitation current, signals are generated in the receiver coils during the relative rotation between rotor and stator, which are a function of the angular position, that is, the relative position between graduation structure and receiver coils. The reason for this has its roots in that the graduation structure influences, thus strengthens or weakens, the magnetic field produced by the excitation current. These signals are then further processed in evaluation electronics.
Such rotary encoders are often used as measuring devices for electric drive systems, to determine the absolute angular position of corresponding drive shafts. In this context, it is important, particularly from the standpoint of safety, that even after the system is shut down or in the event of a power failure, at least the full revolutions executed in this state are counted.
German Published Patent Application No. 197 51 853 describes an arrangement for an inductive rotary encoder, in which the excitation coils and receiver coils are disposed in a multilayer printed circuit board structure.
In order for such a rotary encoder to be able to at least count the number and direction of rotation of the full revolutions covered, even when the system voltage supply is absent, in conventional methods, suitable magnets are provided at the rotor, and two or more magnetic sensors, which generate counting signals, are provided at a stator printed circuit board. In this operating state, the magnetic sensors and evaluation electronics necessary for the counting are powered by a backup battery.
German Published Patent Application No. 10 2006 046 531 describes an inductive rotary encoder, which, upon the absence of a system voltage supply, is able to be operated in an energy-saving mode, in which the rotary encoder is powered by a backup battery. To reduce the energy consumption in this mode, it is proposed to supply only a pulsed excitation current to the excitation coils.